Desulfurization of hydrocarbon gases



May 27, 1952 K. M. BROWN Er AL 2,598,034

nEsuLFLuRIzATIoN oF HYDRocARBoN GASES Filed Jan.v19, 1949 i za 57 Patented May 27, 1952 DESULFURIZATION F GASES HYDROCARBON Kenneth M. Brown, Hinsdale, and Clarence AGr. Gerhold, Riverside, Ill., assignors to Universal Oil Products Company, Chicago ration of Delaware Ill., a corpo- Application January 19, 1949, Serial No. 71,658

The present invention relates to the desulfurization of hydrocarbons and more particularly to the removal of mercaptans by a novel process which minimizes the introduction of water into the hydrocarbon stream.

In many cases it is desired to remove mercaptans from a hydrocarbon stream without at the same time introducing water into the hyldrocarbon stream and this is particularly true in the case of gases which are transported and handled under high pressures. For example, natural gas is usually given a dehydration treatment at the gathering point in a gas producing oil field, the extent of dehydration being controlled to meet a specied dew point. The dew point is predetermined at slightly above the lowest temperature which will be encountered in the transportation and handling of the gas. While some of the mercaptans are removed from the gas during the dehydration treatment, the

4 Claims. (Cl. 260-676) remtaining mercaptan content is in many casesv too high for satisfactory use. However, in removing the mercaptans subsequent to dehydration, care must be observed to preclude the introduction of Water vapor into the gas stream because of the possible formation of solid hydrates due to reaction between the water and hydrocarbons. For this reason, the removal of mercaptans from dehydrated gas by conventional processes cannot be employed because of the fact that such processes are carried out n the presence of water, some of which would become entrained in said gas and thereby raise the dew point to such an extent that solid hydrate formation could take place. 'I'he present invention is directed to a novel method of removing mercaptans without at the same time undergoing the -objection of increasing the moisture content.

In a broad -embodiment the present invention relates to a process for desulfurizing a hydrocarbon stream containing mercaptan which comprises contacting said stream with a water immiscible solvent to extract mercaptan from said stream, separating a desulfurized hydrocarbon stream from solvent containing mercaptan, treating said solvent to reduce its mercaptan content, and recycling at least a portion of the solvent of reduced mercaptan content for further use Within the process.

In a specific embodiment the present invention relates to a process for desulfurizing natural gas containing mercaptan which comprises contacting said natural gas With a liquid hydrocarbon solvent to extract mercaptan from said natural gas, separating desulfurized natural gas from hydrocarbon solvent containing mercaptan, treating said hydrocarbon solvent to remove mercaptan, and recycling at least a portion of the hydrocarbon solvent for further use Within'the process.

'Ihe novelty and utility of the present invention is illustrated further in the accompanying diagrammatic ow drawings which illustrate specific embodiments of the invention. In the interest of simplicity the following description of the drawings will be limited to the treatment of a hydrocarbon gas. Further, in the interest of simplicity, valves, pumps, compressors, mixers and the like have been omitted from the drawings.

Referring to Figure I, a hydrocarbon gas containing mercaptans is introduced to the process through line I and is directed into absorber 2, preferably through a suitable spray arrangement as illustrated at 3. In absorber 2, the hydrocarbon gas is passed countercurrently to a suitable solvent introduced through line 4 and directed through line 5 to absorber 2, preferably through a suitable spray arrangement as illustrated at 6. In absorber 2, all or at least a substantial portion of the mercaptans contained in the hydrocarbon gas stream will be transferred from the gas phase to the solvent liquid phase and thereby removed from the hydrocarbon gas. Similarly, all or a substantial portion of hydrogen sulde, carbon dioxide or the like contained in the hydrocarbon gas will be transferred to the solvent phase and thereby removed from the hydrocarbon gas.

In the case here illustrated, absorber 2 comprises a single vertical vessel, which preferably contains suitable contacting means such 'as bubble trays, bubble decks, side to side pans, etc. and may or may not contain Asuitable packing material such as carbon Raschig rings, glass particles, excelsior, etc. It is understood that two or more absorption zones may be employed and also that mixing and settling zones may tbe used within the scope of the present invenion.

Any suitable solvent which is water immiscible and in which mercaptans are preferentially soluble may be used within the scope of the present invention. A particularly suitable solvent comprises a liquid hydrocarbon fraction and thus may comprise a pentane. hexane, heptane, or octane fraction, aromatics such as benzene, toluene. xylene, etc., higher boiling hydrocarbons, or mixtures thereof. In another embodiment of the invention, the solvent may comprise high boiling alcohols, high boiling ketones, etc. which are substantially water immiscible. In still another embodiment of the invention the solvent may comprise disuldes., either formed within the process as will hereinafter be described in connection with one embodiment of the invention or introduced from an extraneous source.

'Ihe hydrocarbon gas is withdrawn from absorber 2 through line 'I and will contain less mercaptans than contained in the original gas stream chargedl to the process. The solvent containing mercaptans, hydrogen sulde and carbon dioxide, etc. when present is withdrawn from absorber 2 through line 8 and is introduced to H28 removal zone 9, preferably through a suitable spray arrangement as illustrated at I0. Any suitable method of removing hydrogen sulide and carbon dioxide, etc. when present from the solvent may be employed. One particularly suitable method is the non-regenerative caustic process in which caustic is introduced to zone 9 through line I I, preferablyA through a suitable spray arrangement, as illustrated at I2. In View of the fact that the caustic cannot be economically regenerated, usually a low Baume caustic of the order of 5 to 15 Baum is used in this step of the process. Hydrogen sulfide, carbon dioxide, etc. will be absorbed inthe caustic and removed from the lower portion of .zone 9 through line I3, while the solvent, substantially free of hydrogen sulfide, carbon dioxide, etc. is withdrawn from the upper portion of zone 9 through line I4. Other suitable methods of removing hydrogen sulde include the use of alkanol amines and particularly diethanol amine, tripotassium phosphate, etc., and it is understood that zone `Si will comprise suitable equipment both for the absorption or removal of the hydrogen sulfide and for regeneration of the particular reagent used. When the gas stream is substantially free of hydrogen sulde, zone 9 may be omitted andthe solvent may be Supplied .from zone 2 direct to zone I5.

The solvent withdrawn through line I4 from zone 9 will be substantially free of hydrogen sulde, carbon dioxide, etc. but will contain mercaptans and, in accordance with the present invention, is introduced by way of line III to mercaptan extractor I5, preferably through a suitable spray arrangement as illustrated at I6. In zone I6 lthe solvent is passed counter-currently to caustic introduced through lines II and I8 to zone I5, preferably through a suitable spray arrangement as illustrated at I9. The caustic is preferably of 10 to 25 Baume. It is understood that any suitable alkaline reagent which will remove mercaptans from the solvent may be employed Within the scope of the present invention and that the alkaline reagent may include various promoters to increase solubility of the mercaptans in the alkaline reagent. Suitablepromoters include methanol, phenols, cresols, potassium isobutyrate, etc. In place of a-single vertical absorption zone as illustrated in the drawing, it is understood that two or more such zones, or mixing and settling zones may be employed. Likewise, zone I5 preferably contains suitable packing material such as carbon Raschig rings and/or contacting means such as bubble trays, bubble decks, side toside pans, etc.

The solvent substantially free of mercaptans is Withdrawn from the upper portion of zone I5 through line 5 and is returned to absorber -6 for further use within the process. The caustic containing mercaptans in the form of sodium mercaptides is withdrawn from the lower portion of zone I5 through line 25 and is directed through heat exchanger 2I and line 22 to caustic regenerator 23, preferably through a suitable spray arrangement as illustrated at 24, In zone 23 the caustic is regenerated by hydrolysis and stripping to convert the sodium mercaptides to caustic and meroaptans. In the case here illustrated heat is supplied to the lower portion of regenerator 23 by means of reboiler 25. It is understood that any other suitable means of heating the lower portion of zone 23, -such as by direct introduction of steam, etc. may be employed. The regenerated caustic is withdrawn from the lower portion of zone 23 through line 26 and a portion thereof is recycled by way of line 2l through reboiler 25 and line 28 back to zone 23. While the remaining portion may be withdrawn from the process through line 29 preferably at least a portion thereof is recycled by Way of line 30, heat exchanger 2I and lines 3I and I8 back to extractor I5 for further use within the process.

Mercaptans and water evaporated in zonef23 are removed from the upper portion thereof through line 32 and are directed through condenser 33 and line 34 into receiver 35. Mercaptans separate from Water in receiver 35, the mercaptans are withdrawn from the process through line 36, and the water is withdrawn through line 3l. Whileall or a portion ofthe water may be removed from the process through line 38, at least a portion thereofis recycled by way of lines 35 and 21 through reboiler 25 and line 28 to regenerator 23 to serve as a hydrolyzing medium therein.

Figure II of the drawing illustrates another specic embodiment of the invention. In this embodiment the mercaptans are converted into disulfldes, and the disuldes are subsequently separated from the solvent and removed'fromthe process. Referring to Figure II, absorber 52, lines 5I, 54, 55, 5l and 58 and spray arrangements 53 and 56 correspond to absorber 2 and the-similar lines and spray arrangements illustrated inFigure I of the drawing. Similarly HzS removal zone 59, lines 5I and 6-3 and 64 andspray arrangements 60 and 62 correspond to HzS removal zone 9 and similar lines and spray arrangements as illustrated in Figure I. The description hereinbefore 'set forth in connection with `Figure yI applies to zones 52 and 59 of Figure II. .The solvent substantially free of hydrogen sulde, carbon dioxide, etc. but-containing mercaptansris directed by way of line 64 into sweetening'reactor 55. Any suitable sweetening system mayiheused 1n this step of the process, a particularly Vsuitable Sweetening system comprising the vuse .0f copper chloride either as a Xed bed orslurry type of operation. It is understood that any other suitable system in which the vmercaptans are converted to disuldes maybe employed within the scope of the present invention. It is also understood that zone 65 will include lsuitable means for regenerating the treating reagent.

The effluent product from reactor 65,7comprising solvent containing disuldes is withdrawn from the lower portion of zone S5 through line 66 and, while a portion thereof may be removedfrom the process through line 61, at least a portion thereof isdirected through line {S8-and may befrecycled by way of lines 69 and 55 to zone 52 for further use in `the process. As hereinbefore Iset forth, the presence of disuldes is not-.objectionable and, in one embodiment of the inventionrthe solvent itself may comprise a disulfide fraction. In another embodiment of the invention, the solvent containing disuliides is directed by way of line 68 through heat exchanger 10 and line 1l to fractionator 12. In fractionator 12 the disuliides are distilled overhead and removed from zone 12 through line 13 and are passed through condenser 14 and line 15 into receiver 16. Water produced during the sweetening reaction or otherwise introduced in the process is separated in receiver 16 from disulfides. The water is withdrawn from the process through line 11 and the disuldes are withdrawn from receiver 16 through line 18. A portion of the disuldes may be recycled by Way of line 19 to the upper portion of fractionator 12 to serve as a cooling and reiiuxing medium therein. The disuldes may also contain gas dissolved from the gas stream by the solvent, and may be subjected to distillation and stabilization for recovery of such gas by well known means not illustrated. The gas dissolved from the gas stream by the solvent which appears as a gas phase in receiver 16 may be recycled to absorption zone 52 by means of lines 8|, 82, 18, 89 and 5l. When desired, all or a portion of the disuldes may be withdrawn from the process through line 90.

The solvent reduced in disuldes is withdrawn from the lower portion of fractionator 12 by way of line 83, a portion thereof is recycled by way of line 84, reboiler 85 and line 86 to fractionator 12, while the remaining portion may be removed from the process through line 81 but preferably is recycled at least in part through line 88, heat exchanger and lines 89 and 55 to absorber 52 for further use within the process.

As a further precaution to insure that the moisture content of the hydrocarbon gas stream will not be increased, it is within the scope of the present invention to include, when desired, a dehydration step for the recycled solvent being returned by way of line 5 in Figure I or by Way of lines 69 or 89 in Figure II or the fraction being recycled from receiver 16 by way of line 80 as also illustrated in Figure II. The amount of these streams will be considerably smaller than the hydrocarbon gas stream charged to the process. Any suitable dehydration system may be employed including the use of liquids such as diethylene glycol, glycerine, zinc chloride, calcium chloride, etc. or solid materials such as calcium chloride, calcium oxide, silica gel, activated alumina, charcoal, magnesium oxide. etc.

In place of the alkaline reagent as desecribed in connection with Figure I or the copper sweetening as described in connection with Figure II of the drawings for the removal of mercaptans, it is understood that any other suitable system for removing mercaptans from the solvent may be employed within the scope of the present invention. Other suitable but not necessarily equivalent processes for removal or conversion of mercaptans include the well known doctor proc ess, hypochlorite treating, the use of hydrogen uoride, etc. It is understood that the necessary absorption, mixing, settling and regenerating zones will be provided to suit the particular process employed. These processes are well known and do not require detailed description in the present specification.

It is thus seen that the novel process of the present invention oers a method of removing mercaptans from hydrocarbon gas streams without at the same time increasing the moisture content thereof.

We claim as our invention:

1. A process for desulfurizing a hydrocarbon gas stream containing mercaptan which comprises contacting said gas stream with a liquid hydrocarbon solvent to extract mercaptan from said gas stream, separating a desulfurized gas stream from hydrocarbon solvent containing mercaptan, treating said hydrocarbon solvent with copper chloride to convert mei-captan to disulfide, and supplying at least a portion of the hydrocarbon solvent containing disulde to the aforesaid contacting step.

2. The process of claim 1 further characterized in that the hydrocarbon gas stream also contains hydrogen sulde, the hydrocarbon solvent extracts the hydrogen sulde along with the mer captan, the hydrocarbon solvent containing mercaptan and hydrogen sulde is treated to remove hydrogen sulfide prior to treating with copper chloride to convert mercaptan to disulde.

3. A process for desulfurizing a hydrocarbon gas stream containing mercaptan which comprises contacting said gas stream with a liquid hydrocarbon solvent to extract mercaptan from said gas stream, separating a desulfurized gas stream from hydrocarbon solvent containing mercaptan, subjecting the separated solvent to a sweetening treatment to convert mercaptan to disulfide, and supplying at least a portion of the disulfide-containing solvent to the aforesaid contacting step.

4. A process for desulfurizing a hydrocarbon gas stream containing mercaptan which comprises contacting said gas stream with a mercaptan solvent comprising disuldes, separating the resultant mercaptan-containing solvent from the desulfurized gas, converting the mercaptans in the solvent to disuldes, and supplying at least a portion of the latter to the aforesaid contacting step.

KENNETH M. BROWN. CLARENCE G. GERHOLD.

REFERENCES CTED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,785,365 Seil Dec. 16, 1930 1,796,621 Ramage Mar. 17, 1931 1,935,725 Perl Nov. 21, 1933 1,986,228 Seguy Jan. 1, 1935 2,041,364 Miller May 19, 1936 2,146,353 Rosenbaugh Feb. 7, 1939 2,269,467 McCullough Jan. 13, 1942 2,297,650 Frey et al Sept. 29, 1942 2,297,751 Dryer et al Oct.,6, 1942 2,311,342 Kerns Feb. 16, 1943 2,312,820 Henderson M-ar. 2, 1943 2,383,416 Reed Aug. 21, 1945 2,395,509 Shaw Feb. 26, 1946 2,411,105 Nixon et al Nov. 12, 1946 2,434,868 Sample et al. Jan. 20, 1948 

4. A PROCESS FOR DESULFURIZING A HYDROCARBON GAS STREAM CONTAINING MERCAPTAN WHICH COMPRISES CONTACTING SAID GAS STREAM WITH A MERCAPTAN SOLVENT COMPRISES DISULFIDES, SEPARATING THE RESULTANT MERCAPTAN-CONTAINING SOLVENT FROM THE DESULFURIZED GAS, CONVERTING THE MERCAPTANS IN THE SOLVENT TO DISULFIDES, AND SUPPLYING AT LEAST A PORTION OF THE LATTER TO THE AFORESAID CONTACTING STEP. 